1. Field of the Invention
The present invention relates to the manufacture of books and particularly to the application of overlays to the cover boards of hard cover books. More specifically, this invention is directed to wrapping apparatus for book cover production machines and especially to apparatus for folding the overlay material, which projects beyond the leading and trailing edges of a cover board, around the said edges and holding the thus folded overlay in contact with the continuously moving board. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
U.S. Pat. No. 2,749,967 discloses apparatus for use in the production of book covers wherein the wrapping of the overlay material around the edges of the backing board, the backing board and overlay moving continuously along a conveyor system, is accomplished by wrapping the side edges prior to the wrapping of the leading and trailing edges. In the patented apparatus, in order to accomplish wrapping of the side edges, the cover units comprising the board and an oversize overlay which has previously been bonded thereto are clamped and fed through the apparatus by transport chains. The overlay is first turned upwardly and subsequently folded back around the board side edges by means of wrapping shafts which travel with the cover units, the wrapping shafts being movable inwardly with respect to the cover unit. Subsequently, the cover units, supported on an endless and continuously moving transport belt, are delivered to a folding mechanism which is installed above the movement path defined by the belt. The folding mechanism, which can be selectively translated into the path of movement of the cover units, wraps the overlay around the leading edge of the board. This wrapping is accomplished by the use of wrapping fingers which are positioned transversely with respect to the direction of movement of the cover unit. The wrapping fingers are mounted side-by-side on a shaft and are spring loaded so as to rest against a hold-down shaft when in the retracted position. The wrapping fingers are lifted against their spring bias by the moving cover units so as to be swung upwardly and out of the plane in which the cover units move.
Continuing to discuss the apparatus of U.S. Pat. No. 2,749,967, as a result of the movement of the wrapping fingers around the leading edge of a cover unit, the overhanging overlay material is folded around the leading edge of the board. The folded overlay is then pressed into contact with the board by means of pressure rollers which follow the wrapping fingers. The trailing edges of the cover boards are wrapped in an analogous manner, but by means of wrapping rails that are installed on driven chains which move on endless paths. These wrapping rails are propelled, for a short period, at a speed in excess of that at which the cover units move. The wrapping rails, when overtaking the moving cover unit, come to bear thereagainst and i so doing overcome a spring force. In order to prevent the action of the trailing edge wrapping rail from pushing the cover unit forwardly, motion retarding fingers which act on the leading edge of the cover are provided. Pressure rollers, resiliently mounted at locations such that they follow the wrapping rail, serve to press the overlay material against the board once the folding action has been accomplished by the rail.
The above briefly described book cover production machine has a number of disadvantages. By way of example, the wrapping fingers rock relatively rapidly around the cover board edge with the result that the overlay material is neither pressed flat against the leading edge nor is it held against the edge or the surface of the board to which the overlay is to be adhered. Thus, the desired, taut folding of the overlay material around the board edges cannot be achieved with apparatus of the type disclosed in U.S. Pat. No. 2,749,967, this being particularly true when employing overlay materials which are relatively stiff. The foregoing deficiency is, in large measure, attributable to the relatively small contact pressures exerted by the wrapping fingers. However, applying a greater pressure through the use of stronger spring elements would not solve the problem since the spring forces must be overcome by the moving cover unit and the possibility of damage to the overlay material increases significantly as the spring force which must be overcome increases.
It is also to be noted that, in the case of a wrapping apparatus of the type disclosed in U.S. Pat. No. 2,749,967, the wrap-folded overlay material is not held firmly against the cover board for a defined period of time. The maintaining of pressure against the wrap-folded overlay material for an "initial bonding time" is an absolute necessity if adhesive-bonding is to be reliably achieved. The period of time during which the pressure must be maintained is a function of the type of adhesive used, the thickness of the adhesive applied and the nature of the overlay material and cover board being processed. The initial bonding time of the adhesive becomes particularly important if the production rate of the wrapping apparatus is increased and/or if stiff overlay materials such as "Balacron" or "Skivertex" are used.
Continuing to discuss the problem of insuring reliable adhesive bonding, the consequence of a pressing time for the wrap-folded overlay material which is too short is that the overlay material will subsequently separate from the cover board. Any such separation is the cause of significant production problems, particularly during the operations which must subsequently be performed on the cover unit such as pulling-in the corners and wrapping the side edges.
To summarize the above discussion, prior art wrapping techniques and apparatus as exemplified by the disclosure of U.S. Pat. No. 2,749,967 are incapable of achieving the sharp-edged finish that is desired in book cover production and such prior apparatus and techniques often result in air entrapment between the overlay material and the cover board, hollow edges and wrap separation.
Another example of a prior art method and apparatus for use in the manufacture of book covers, particularly for wrapping overlay material around cover boards, may be seen from U.S. Pat. No. 2,667,909. In the apparatus of U.S. Pat. No. 2,667,909 the cover units, comprising the overlay material pre-bonded to the cover boards, are caused to move through a pair of cylindrical segments. During the course of this movement, the overlay material that projects beyond the cover board leading edge is first folded downwardly through the action of a folder plate installed in the upper cylindrical segment. The downwardly folded overlay material is caused to emerge through an aperture under the influence of control devices and is subsequently held in the folded position by the action of an air blast. The folded flap is subsequently pressed against the cover board as the moving cover unit passes between pressure rollers. In order to wrap the trailing edge of the cover unit, a second folder plate is installed in the upper cylindrical segment and, under the influence of a control device, produces the downward folding of the overlay material which projects beyond the trailing edge of the cover board. The lower cylindrical segment has a driving plate which is movable in the direction of travel of the cover unit. This driving plate further folds the overlay material and presses it firmly against the cover board from below until the cover unit is received between the pressure rollers.
Apparatus of the type disclosed in U.S. Pat. No. 2,667,909 cannot achieve the "initial bonding time" since neither the folder plates, which are moved relatively rapidly past the board edges, for the pressure rollers, which act only briefly on the cover unit, are designed to maintain their pressure for an extended period of time.
It is also to be noted that, in apparatus of the type exemplified by U.S. Pat. No. 2,667,909, only small push forces are exerted by the folder plates as they move past the cover board edges and these forces are insufficient to pull the overlay materials tautly around the board edges, this being particularly true if the overlay materials are relatively stiff. Similarly, this type of prior art apparatus is also incapable of achieving the sharp-edged finish, free of air pockets and hollow edges, which is desired. This is particularly true in the case of the leading-edge wrapping operation in which merely an air blast is used for holding the folded wrapping material.